RFR: 8256633: Fix product build on Windows+Arm64

[Bernhard Urban-Forster]

Fix this warning:
C:\work\openjdk-jdk\src\hotspot\cpu\aarch64\assembler_aarch64.hpp(508): error C2220: the following warning is treated as an error
C:\work\openjdk-jdk\src\hotspot\cpu\aarch64\assembler_aarch64.hpp(508): warning C4390: ';': empty controlled statement found; is this the intent?

Thanks to @magicus to bring that to my attention.

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Commit messages:
 - 8256633: Fix product build on Windows+Arm64

Changes: https://git.openjdk.java.net/jdk/pull/1312/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1312&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256633
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1312.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1312/head:pull/1312

PR: https://git.openjdk.java.net/jdk/pull/1312